Parkinson's disease (PD) is a progressive degenerative disease of the central nervous system. The risk of developing Parkinson's disease increases with age, and afflicted individuals are usually adults over 40. Parkinson's disease occurs in all parts of the world, and affects more than 1.5 million individuals in the United States alone.
While the primary cause of Parkinson's disease is not known, it is characterized by degeneration of dopaminergic neurons of the substantia nigra. The substantia nigra is a portion of the lower brain, or brain stem that helps control voluntary movements. The shortage of dopamine in the brain caused by the loss of these neurons is believed to cause the observable disease symptoms.
The symptoms of PD vary from patient to patient. The most common symptom is a paucity of movement and rigidity, characterized by an increased stiffness of voluntary skeletal muscles. Additional symptoms include resting tremor, bradykinesia (slowness of movement), poor balance, and walking problems. Common secondary symptoms include depression, sleep disturbance, dizziness, stooped posture, dementia, problems with speech, breathing, and swallowing. The symptoms become progressively worse with time and ultimately result in death.
A variety of therapeutic treatments for PD are available. Perhaps the best known is levodopa, a dopamine precursor. While levodopa administration can result in a dramatic improvement in symptoms, patients can experience serious side-effects, including nausea and vomiting. Moreover, many patients develop involuntary choreiform movements which are the result of excessive activation of dopamine receptors. These movements usually affect the face and limbs and can become very severe. Such movements disappear if the dose of dopamine precursor (e.g., levodopa) or dopamine agonist is reduced, but this typically causes rigidity to return. Moreover, the margin between the beneficial and the unwanted effects (i.e., the therapeutic window) appears to become progressively narrower as the period of treatment lengthens.
A further complication of long-term treatment with certain dopamine receptor modulators (e.g., dopamine precursors or agonists) is the development of rapid fluctuations in clinical state where the patient switches suddenly between mobility and immobility for periods ranging from a few minutes to a few hours. The fluctuations are of several general types. “Wearing-off” phenomena are deteriorations in the relief afforded by a dose of levodopa before the next dose takes effect (Van Laar T., CNS Drugs, 17:475, 2003). Because they are related to a patient's dose schedule, such periods are often relatively predictable (Dewey RB Jr., Neurology, 62(suppl 4):S3-S7, 2004). In contrast, “on-off” phenomena are sudden transitions from an “on” period of levodopa benefit to an “off” period of akinesia, rigidity, and tremor that occur in minutes or even seconds, (Swope DM., Neurology, 62(suppl 4):S27-S31 (2004)) with no discernible relation to a patient's dose schedule. Two other phenomena are the delayed “on” effect, in which levodopa's effects are substantially delayed, and dose failure (also known as the no-“on” or skipped-dose effect), in which no effects occur at all. These various “off” states can produce such an abrupt loss of mobility that the patient may suddenly stop while walking or be unable to rise from a chair in which he had sat down normally a few moments earlier.
Subcutaneous injections of apomorphine have proved to be effective in the treatment of “on-off” fluctuations in Parkinson's disease within 7 to 23 minutes, and last for 45 to 90 minutes. Trials have shown consistent reversal of “off” period akinesia. Advantages over other dopamine agonists include a quick onset of action and lower incidence of psychological complications. For a “rescue therapy” in patients with “on-off” fluctuations, apomorphine also has the advantage over other dopamine agonists, as it has a relatively short half-life.
Numerous formulations and routes of administration for apomorphine have been studied and apomorphine therapy has been found to be hampered by various complications. For example, oral administration of apomorphine tablets has required high doses to achieve the necessary therapeutic effect because apomorphine administered by this route undergoes extensive metabolism in the small intestine and/or, upon absorption, in the liver; sublingual administration of apomorphine tablets caused severe stomatitis on prolonged use with buccal mucosal ulceration in half the patients treated (see Deffond et al., J. Neurol. Neurosurg. Psychiatry 56:101, 1993); and intranasal administration produced transient nasal blockage, burning sensation and swollen nose and lips (see Koller et al., Neurology 62:S22, 2004). While subcutaneous injections of apomorphine have proven effective, an injection by needle is difficult for Parkinson's patients because of impaired motor function. Furthermore, a common side effect of subcutaneous injection is the development of nodules, which often become infected, necessitating antiobiotic treatment or surgical debridement (see Prietz et al., J. Neurol. Neurosurg. Psychiatry 65:709, 1998).
There is a need for new apomorphine regimens which are safe, effective, and easy for a Parkinson's patient to use. In particular, there is a need for the regimens that are efficacious in a wide patient population while reducing the possibility for adverse events.